This invention relates in general to optical oximeters and relates more particularly to an adapter that enables an optical oximeter probe, that is designed/configured to be utilized on an associated oximeter/monitor, to be used on a different oximeter/monitor that utilizes a different probe configuration.
Because of the importance of oxygen for healthy human metabolism, it is important to be able to measure the oxygen content of a patient""s blood. The monitoring of a patient""s arterial hemoglobin oxygen saturation during and after surgery is particularly critical.
Noninvasive oximeters have been developed that direct light through a patient""s skin into a region, such as a finger, containing arterial blood. This light typically contains two or more primary wavelengths of light. Examples of such oximeters are disclosed in U.S. Pat. No. 5,209,230 entitled xe2x80x9cAdhesive Pulse Oximeter Sensor With Reusable Portionxe2x80x9d issued to Swedlow, et al. and in U.S. Pat. No. 4,700,708 entitled xe2x80x9cCalibrated Optical Oximeter Probexe2x80x9d issued to New, Jr. et al., both assigned to the assignee of the present invention, the disclosures of which are incorporated herein by reference. The oximeter in the patent by New, Jr. et al. includes a probe that contains a resistor having a resistance that can be measured by a monitor to which the probe is attached. The measured value of this resistance is indicative of the wavelengths of the light directed from the light emitting diodes (LEDs) through the patient""s epidermis. The monitor uses this information and the measured intensities of light detected at those wavelengths to calculate the blood arterial oxygen content of the patient. The LEDs are typically activated in non-overlapping temporal intervals, so that the amount of absorption of light at each of these two wavelengths is usually measured separately.
Oftentimes, an oximeter sensor may be made by one manufacturer, and a monitor by another manufacturer. Accordingly, adapters may be necessary if the sensor and the oximeter/monitor are not compatible. Alternately, the sensor itself can be configured so that it can be used with different oximeters. For example, U.S. Pat. No. 5,249,576, entitled xe2x80x9cUniversal Pulse Oximeter Probexe2x80x9d issued to Goldberger et al., allows the leads of the sensor to be connected in alternate configurations. Examples of adapters are set forth in U.S. Pat. No. 5,807,247, assignee Nellcor Puritan Bennett, Inc., and in U.S. Pat. No. 5,818,985, also assigned to Nellcor Puritan Bennett, Inc. Yet another adapter is set forth in copending application No. 09/040,218, filed Mar. 17, 1998, entitled xe2x80x9cActive Optical Oximeter Probe Adapterxe2x80x9d, Adnan Merchant et al., also assigned to Nellcor Puritan Bennett, Inc. The disclosures of all three of the above Nellcor Puritan Bennett applications are incorporated herein by reference.
In one type of oximeter sensor, set forth in Masimo Corporation U.S. Pat. No. 5,758,644, separate leads on the sensor for connecting to a coding resistor are eliminated. Instead, the coding resistor is connected in parallel with the light-emitting diodes (LEDs) of the sensor. The coding resistor can be read by providing a low voltage at which the LEDs will not conduct substantial current. For example, a voltage of 0.5 volts will accomplish this. Thus, in a configuration mode, a low voltage can be driven to the LED leads, and the resistance can be read. Subsequently, higher voltages can be used for driving the LEDs in an operational mode. Clearly, oximeter sensors without such a resistance across the LED leads will not be compatible with such an arrangement. In one embodiment of the Masimo sensor, the resistor does not provide a coding function at all, but rather modifies the characteristics of the LEDs.
The present invention provides an oximeter sensor adapter which allows a sensor without a resistor in parallel with its LEDs to operate with an oximeter expecting such a resistor in parallel. The adapter has a switching circuit which has inputs connected to the LED drive outputs of the oximeter. The switching circuit has two pairs of outputs, one connected to the LED drive lines of the sensor, and the other connected to a resistor in the adapter itself. The switching circuit is controlled by a sensing circuit which senses when a signal on the input lines drops below a predetermined level, such as 0.5 volts. The sensing circuit, in response to a low voltage (corresponding to an attempt to read a resistor in parallel with the LEDs), will provide a signal to a switching circuit. The switching circuit will switch the resistor onto the input lines so that it can be read. When a higher voltage returns to the input lines, the switching circuit switches back to the LEDs themselves.
Thus, the present invention in essence fools the oximeter into thinking that there is a resistor connected in parallel with the LEDs, when in fact there is not. It allows a sensor without a resistor across its LED leads to work with an oximeter expecting such a resistor.
For a further understanding of the nature and advantages of the invention, reference should be made to the following description taken in conjunction with the accompanying drawings.